The invention relates to a system for determining the duration of injection-control commands to be applied to fuel injection valves associated with an internal combustion engine, the duration of the fuel injection depending, among other factors, on the rpm, the airflow rate in the suction tube and the temperature of the internal combustion engine. The airflow rate is monitored by an airflow meter generating a proportional output voltage, while a temperature sensor close to the engine monitors engine temperature, and a tachometer monitors engine rpm. Furthermore, a computer circuit utilizes the rpm, temperature and airflow rate data and calculates from such data the duration (ti) of the injection pulses.
In a known fuel injection system for controlling at least one injection valve of an internal combustion engine as a function of the airflow rate, DC signals are formed in a computer circuit which are proportional to the airflow rate and to crankshaft rpm. These signals are further processed as analog signals in DC amplifier stages. In such analog computers the latter must be balanced very precisely, because difficulties can arise with respect to long-term drift. Also, such analog computers are sensitive to interference pulses. Difficulties do arise on that account especially when these types of devices are used with motor vehicles. For example, the ignition system or the system producing the directional signals in the motor vehicle can give rise to such interfering pulses, which are beyond control.